Augmented reality, also commonly referred to as augmented vision or augmented reality vision, augments an observer's view of the real world by superimposing computer generated graphical information. This information may be as simple as a text label attached to some object in the scene, or as complex as a 3D model of a patient's brain derived from an MRI scan and aligned to the real view of the person's head.
The observer may observe a real scene directly with his or her eyes, with the additional graphical information being blended therewith via a semi-transparent display located between the observer and the real scene. Such a display device can be, for example, a see-through head mounted display.
The display can also be opaque, like a computer screen or a non-see-through head mounted display. Such a display then presents to the observer the complete augmented view, i.e., a combination of the real-world view and the graphics overlay. A video camera takes the place of the real-world observer to capture the real world-view. For stereo vision, two cameras are required. A computer is used to combine the live video with the graphics augmentation.
The graphics have to be positioned, oriented, and scaled, or even rendered in a perspective fashion for correct alignment with the real-world view. It is desirable to “anchor” the graphics to a real-world object. To do this, the position and orientation of the camera with respect to the object, as well as the orientation of the object, must be known. That is, the relationship between two coordinate systems, one corresponding to the camera and the other corresponding to the object, must be known.
Tracking denotes the process of keeping track of the preceding relationship. Commercial tracking systems are available that are based on optical, mechanical, magnetic, inertial, and ultrasound measurement principles.
Augmented reality visualization can guide a user in manual mechanical tasks. For machine repair and maintenance scenarios, it has been suggested to augment the view with graphical pointers that show, e.g., which button to press or which screw to turn. Augmented reality visualization is also being suggested for medical applications where, e.g., biopsy needles have to be inserted into a target tumor without harming nearby nerves or where screws have to be inserted into bones at a precise location and in a precise direction.
As noted above, augmented reality visualization places virtual objects (computer generated graphics) into real scenes. The tracking of the vantage point, from which the real scene is viewed, with respect to a world coordinate system anchored at real world objects, allows the virtual objects to appear at desired locations in this world coordinate system. However, a correct visual interaction between real and virtual objects generally requires 3D information about the real objects. Disadvantageously, this 3D information is usually not available and, thus, the virtual objects are simply superimposed onto the image of the real scene. Accordingly, real objects can be hidden by virtual objects, although virtual objects cannot be hidden by real objects.
In addition, in medical applications there is an issue when a needle needs to be inserted in a procedure, such as a biopsy, that the needle takes a direct route to the target object without intersecting delicate structures, such as arteries or organs not of interest. In order for the physician to accurately guide the needle, it would be advantageous for the physician to know what potential obstacles are in its path. Accordingly, it would be desirable and highly advantageous to have a method for augmented reality instrument navigation so that the physician can determine an optimal path prior to insertion of a needle or other medical instrument.